The development of natural, multi-mechanistic anti-obesity strategies remains a critical need in nutritional science. While lactic acid bacteria (LAB) show probiotic promise, their full potential, particularly regarding non-viable forms and metabolites, is not fully realized. This study establishes a complete pipeline from strain screening to practical application, highlighting their multifunctional role in lipid metabolism. We performed comprehensive in vitro screening of LAB strains (including Lactiplantibacillus plantarum, Pediococcus acidilactici, Enterococcus faecalis, and Ligilactobacillus animalis) for cholesterol assimilation and bile salt deconjugation. Genomic analysis of selected strains confirmed functional genes and importantly, revealed an absence of virulence factors, ensuring their safety profile. Beyond conventional probiotics, we systematically investigated live bacteria, heat-inactivated cells (postbiotics), and capsular polysaccharide (CPS). The application and efficacy were then rigorously evaluated in vivo across diverse models of obesity (obese mice, laying hens). The results demonstrated that administration of these multifunctional LAB preparations significantly alleviated obesity phenotypes, improved blood lipid profiles, and reduced hepatic steatosis. Crucially, we confirmed that the beneficial effects were not exclusive to live bacteria, as inactivated forms and purified CPS also exhibited substantial lipid-modulating activities, underscoring a multi-factorial mechanism of action. In conclusion, our findings unveil the robust anti-obesity properties of the selected LAB strains. We demonstrate that the beneficial effects are mediated through multiple forms—live, inactivated, and their bioactive metabolites. This holistic study, from in vitro screening to multi-model in vivo validation, provides a solid scientific foundation for developing novel LAB-based strategies, including next-generation postbiotics, for combating obesity and metabolic syndromes.